Space discharge tube and electrode



Jan. 11, 1949.

C. P. BOUCHER SPACE DISCHARGE TUBE AND ELECTRODE THEREFOR Original FiledSept. 14, 1942 Qwuwvtcvo CHARLES E BoucHER,

Reiccued Jan. 11, 1949' THEREFOR.

Charles Philippe Boucher, deceased,'lat ejof Newark, N. J., by NationalInventions Corporation,

New York, asslgnec Original No. 2,384,007, dated "September 4, 1945,

N. Y., a corporationolliew Jersey,

Serial No. 458,273, September 14', I942. Application for reissue August30, 1946, Serial No.

5 Claims. 1

The invention relates to space discharge tubes, and more particularly tofilamentary electrodes for such tubes.

An object of the invention is the provision of electrodes suitable foruse in space discharge tubes operating on cold-cathode, which electrodesare characterized by their resistance to detrimental efl'ects of highpeak voltages and currents, and which are simple, sturdy, reliable andefficient, of low over-all and minimum cost, and of long useful life.

Another object of the invention is the provision of an electrode of thetype described which is characterized by its high electron-emittingqualities, by its uniform emissive qualities throughout useful life,which functions at uniform potential throughout the length ofits'included filament,- which displays substantially the same physicalstrength at all points and is free of predictable zones'ofdeterioration, which electrode is resistant against tearing ofelectron-emitting material therefrom during operation, and which permitsin general the achievement of better operation of an associated tubestructure, as well as the enjoyment of longer tube life- Other objectsand advantages of the invention will in part be obvious and in partpointed out hereinafter in connection with the following description,taken in light of the accompanying drawing.

The invention, accordingly, resides in the several elements, features ofconstruction and operational steps, and in the relation of 'each of thesame to one or more of the others, all as described herein, the scope ofthe application of which is indicated in-the appended claims.

In the single figure of the drawing, there is shown in perspective viewa preferred embodiment of the filamentary electrode of the invention.

coating as is customary practice at this time, tube operation isreasonably insured almost regardless of the pressure conditionsmaintaining within the tube.

A conventional filamentary electrode usually takes the form of asubstantially U-shaped member, shaped from small-diameter, oxide-coatedwire spiraled into comparatively large loops. The end portions of thewire are connected at terminals tosuitable current leads. A source ofelectrical energy connected across the leads, sends heating currentthrough the filament and raises the same to a temperature at whichcopious quantitles of electrons are emitted.

Experience shows, however, that in many instances, an are betweenpaired, spaced electrodes tends to settle across points on theelectrodes of lowest potential dfierence. This action, of course,exposes those points to excessive disintegration. Alternatively, in manyinstances, the arc settles on sharp, angular portions of the filaments,as

at corners or bends. The arc locally attacks the filaments at thesepoints much more vigorously than it does the remaining portions, so thatcomparatively early failure may reasonably be anticipated. Such localfailure is accelerated particularly in those cases where, in accordancewith recent practice, the electrode terminals are shortcircuited forcold-cathode operation, and substantial potentials are impressed acrossthe paired electrodes, such as 460 volts or more.

Similarly, bare filamentary electrodes when unprotected by any form ofshielding are affected seriously and adversely under repeatedbombardment of the are, as when the lamp is turned on and offfrequently. It is found that ionic bombardment results in sputtering ofthe electrode material. When sputtering occurs not only is the activematerial removed from the electrode filaments so that itselectron-emitting qualities are impaired, but as well, the filaments arephysically weakened, thus diminishing appreciably the effective lifethereof. The sputtered or volatized electrode material deposits as acondensate on the interior walls of the tube in which the electrodes aremounted, forming a semi-opaque coating and materially reducing thetransmission of light through the tube walls. This gives rise to thephenomenon encountered in the tube art of darkening of the tubes duringuse.

The use has been proposed of filament guards, but such guards asheretofore employed have not proven successful in hot-cathode tubesadapted for cold-cathode operation. The are has been found to strikerather indiscriminately on the guards or on the filament. The filamentis subjected to shock, breakdown and failure at the corners, bends, orpoints of lowest voltage. In those instances where the arc does strikefirst on the guards, then the are often is found to move relativelyslowly from the guards over to the filaments, so that an appreciabletime interval is interposed before the tube comes up to its rated lightemission.

A further object of the invention, therefore, is to provide filamentaryelectrodes which are suitable for cold-cathode operation, thefilamentary portions of which in large measure are protected from shock,sputtering, and attendant destruction, which electrodes ensure rapid andsteady operation of an associated tube and are instrumental in achievingimproved light emission, and which avoid in large measure or minimizeappreciably other defects and disadvantages set forth in the foregoing.

Referring now more particularly to a preferred embodiment of theinvention, attention is directed to the single figureof the drawing,wherein is shown a tube electrode having a filament or centralfilamentary portion I3. The filament I3 is made, for example, oftungsten, molybdenum, or other suitable refractory metal or metal alloywire of approximately No. 42 gauge. The wire, as shown, is doublycoiled, first into small diameter spiral loops and then into spiralloops of larger diameter. By virtue of the double coiling a large areaof filament is presented per unit of length. This filament l3 has itsends l4, l5, and mid-portion 35 Joined respectively, as by welding, toleads l6, l1, and central support I8. The leads and central supportextend upwardly from the filament l3 and preferably are normal to thefilament and in the same plane therewith. The leads, as well as thecentral support, are made of rather large diameter wire as compared tothe filament, and serve to hold the filament in substantially straightposition. Thus, the presence of angular bends is avoided in the activefilament ii of the new electrode construction and longer life of thefilament or electrode, as a whole, accordingly is achieved.

After the filament I3 is anchored to the leads and to support I 8, thefilament is coated as well as the anchor points with an oxide-coating ofhigh electron-emitting properties. The purpose of the oxide coating (orother electron-emitting material) is, of course, to ensure thatsufiicient electrons will be emitted to initiate and maintain asatisfactory tube arc, without requiring the central portion l3 to bebrought to full incandescence.

The new electrode, aside from including a filament disposed on asubstantially straight axis between leads l6 and I1, is furtherprotected from disintegration and from developing local regions ofpossible failure, by ensuring that all parts of the filament l3 are atsubstantially the same potential. This end is achieved byshortcircuiting the leads I 8, l1 and support is by any suitableshort-circuiting bar or element 19, disposed either at free ends ofthese elements or preferably intermediate their lengths. In this mannerit is ensured that voltage distribution throughout the electrodeassembly is uniform. The end of support l8, opposite from the filamentI3, terminates, for example, in a conventional glass press 32 of glasstube 34, while the leads l5, l1 are either carried through the press, ordirectly through the reentrant portion 33 of the tube.

Still further, protection is afforded the filament l3 by the provisionof a guard in the form of side-arms indicated generally at 20, 2|,attached to and projectin respectively from leads l6, l1. While theseside-arms 20, 2| could be attached at anchor points ll, I5, it isundesirable to have 4 the arc, which strikes on the side-arms 20, 2|,transferred to the central portion II at these anchor points because ofthe possibility of local attack. Accordingly, it is preferred to jointhe sidearms 20, 2| to leads I8, II at points 22, 23 intermediate thelengths of the leads.

Referring first to side arm Ill, this side-arm extends, for example,outwardly at 24 in the plane of lead l6 and filament I3 and normally tolead l8, then is bent into a portion 25 extending out of the plane oflead II and filament ll, then is bent into a portion II which extendssubstantially parallel with lead 16 and below the central portion I! (inthe direction of an opposed electrode, not shown) and finally is bentinto portion 21 which extends in spaced, offset and substantiallyparallel relation with central portion I! so as to guard the same.

Similarly, side-arm 2| extends, for example, outwardly at 28 in theplane of lead i1 and filament I3 and normally to lead I1, then is bentinto a'portion 29 which extends out of the plane of lead l1 and filamentI! in an opposite direction to portion 25 of guard 20. The guard then isbent into a portion ill which extends substantially parallel with leadl1 and below central portion l3 preferably to a point below side-armportion 21 of side-arm 20, and finally is bent into portion 3| whichextends in spaced, substantially parallel relation with filament l3 andportion 21. Side-arm portions 21, 3|, accordingly, are disposed onopposite sides of filament l3 and are substantially parallel with eachother. The portions '21, 3|, preferably reach individually along theentire length of filament II, or are of such length as to overlap inreach along the length of the filament.

While it is not essentialthat the side-arms 20 2| be so constructed, itis preferred to form them of strong heavy gauge wire, to provide a largearea on which the effect of the tube are striking thereon may bedistributed. The wire preferably is made of metal or metal alloy, suchas iron or stainless steel, which with increase in temperature displayson increase in electrical resistance, or, in other words, which displaysa high temperature coefficient of resistance.

When a sumciently high potential is first established across a spacedischarge tube employing electrodes constructed in accordance with theinvention, the gas filling of the tube becomes excited and an arcsettles quickly on one or both of the prong portions 21, ll of thecorresponding overlapping side-arms. At all times, the filamentarycentral portion it will be effectively shielded and protected frominitial shock attendant upon striking the arc., By forming the sidearms, 20, 2| of material having high resistance characteristics, asaforesaid, the resistance of the side-arms increases appreciably withrise in the temperature thereof. The arc, accordingly, migrates rapidlyup the side-arms to the corresponding lead IE or IT, and thence down tothe central portion l3, where it settles for steady operation. In thismanner, it is ensured that the tube quickly approaches conditions ofmaximum luminosity, upon closure of the primary energizing circuit.

A fluorescent tube including two of the new electrodes and otherwiseconstructed along conventional lines, was tested on cold-cathodeoperation, using a 460 volt power unit. The tube was found to have alife approximating 3000 hours. In running life tests on the new tubeunit, a check test was run on a hot-cathode tube of conventional design.This tube was short-circuited at its hot-cathode terminals, to adapt thesame for cold-cathode operation. A power unit of the type just mentionedwas employed under precisely the same energizing conditions as before.The tube thus operated displayed a life of approximately 2000 hours.

In another series of tests, two high voltage power units each having acondensive side (supplying a leading current) and an inductive side(supplying a lagging current), were connected in parallel at their inputsides and operated from the same switch, so that voltage and temperatureconditions and irregularities of the primary circuit would be the samefor both units. One of the power units was connected with two tubesemploying the new electrode construction. Two ordinary 40 watt tubes ofstandard design, now on the market and made by one of the largermanufacturers, but with their terminals shortcircuited, were placedacross the other power unit. The current was made and broken some 276times per hour.

During the'eourse of the test it was observed that the lamp energizedacross the condensive side of the corresponding power unit, tailed after29,256 cycles 01' on'and ofi operation. The other lamp, energized on theinductive side of the power unit, still was in excellent condition, itbeing conservatively estimated that it could have withstood anadditional 4000 to 500;; cycles of striking.

By contrast, the first of the lamps of conventional design placed acrossthe condensive side of the second power unit needed replacement afterabout 12,834 cycles of operation. The second lamp, connected across theinductive side, secquired replacement after 18,147 cycles of operation.A third similar lamp, provided on the condensive side and replacing thefirst said lamp, was in turn worn out after 16,148 cycles or operation.It would appear that under comparable conditions of test, the new lampmay be expected to display a life 01' approximately double that of priorknown lamps under similar operating conditions. Thenew lamp may beexpected to display a practical life 01 2800 hours, with at least 2500hours minimum. The lamps can be produced without difliculty, and withthe electrodes properly constructed, it is safe to predict that theminimum life 01' the commercial form of tubes employing my new filamentmay be raised to 3000 hours.

Thus it will be seen that there has been provided in this inventionimproved filamentary electrodes in which the various objectshereinbefore noted, together with many thoroughly practical advantages,are successfully achieved. It will be seen i'urther that the electrodeslend themselves to durable, eiiicient and economical use in gaseousdischarge tubes operated on coldcathode. It will also be seen that thefilaments my electrodes individually are maintained at uniform potentialthroughout, are tree of angular bends or projections, and are guardedefi'ectlvely against sudden bombardment or shock, so as to avoiddisintegration or sputtering either locally or generally.

As many possible embodiments may be made 01' the invention and as manychanges may be made in the embodiment hereinbetore set forth, it is tobe understood that all matter described herein is to be interpneted asillustrative and not in a limiting sense.

What is claimed is:

1. An electrode comprising a filament made of doubly coiled small gauge,oxide-coated wire, leads extending from the ends of said filament, aguard comprising side-arms, of heavy gauge metal of high temperaturecoeiiicient of resistance, extending outwardly and downwardly from saidleads and under and along the length of said filament in spaced parallelrelation thereto, and means short-circuiting said leads.

2. An electrode for space discharge tubes, comprising, a substantiallylinear filamentary portion; current leads extending from the ends ofsaid filamentary portion; and a support wire extending from anintermediate point along said filamentary portion, said leads and saidsupport wire being short-circuited.

3. An electrode for space discharge tubes comprising, a filamentary,electron-emitting portion;

leads extending upwardly from opposite ends of said filamentary portion;a support wire extending upwardly from said filamentary positionintermediate the ends thereof, said leads and said support wire beingshort-circuited; and a guard comprising side-arms extending outwardlyfrom said leads intermediate their lengths and downwardly tosubstantially parallel guarding position with respect to saidfilamentary portion.

4. An electrode for space discharge tubes cornprising, in combination,an oxide-coated filament, a guard having a side-arm of high temperaturecoefiicient of electrical resistance positioned adjacent said filamentand in electrical connection therewith, and means permanentlyshort-circuit said filament and said guard.

5. A gaseous tube having a filament therein and having currentconducting leads attached thereto and extending through a wall of thetube, and a short-circuiting bar connected across said leadsintermediate their lengths.

NATIONAL INVENTIONS CORPORATION,

Assignee of Charles Philippe Boucher, Deceased,

BY FREDERICK H. SKROTZKI, Vice-President.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

